176 ARGUMENTS: MONOTHEISTIC CONCEPTIONSDefinition 6: A being has maximal excellence if and only if it is
omnipotent, omniscient, and omnibenevolent in some
possible world.
Definition 7: A being has maximal greatness if and only if it has
maximal excellence in every possible world.
Definition 8: A proposition is true in all possible worlds if and only if
it is necessarily true.^10
There are various versions of the Ontological Argument. Here is one:
A God is a perfect being.
B A perfect being has all perfections.
C Having logically necessary existence is a perfection.
D God has logically necessary existence (from A, B, C).
E If God has logically necessary existence then God exists is necessarily
true.
F God exists is necessarily true (from D, E).
While it has played a significant role in the history of philosophy, it remains
true that the notion of perfection is hard to define with any precision. If the
argument can be stated without appeal to this notion, so much the better. In
fact, it can be so stated, and if the argument stated without the notion of a
perfection fails, then so does the argument stated with that notion.
The Ontological Argument without the notion of perfection
Here is a formulation that makes no appeal to the notion of a perfection,
though it does include certain central concepts that express what the
tradition plausibly thinks are qualities that a perfect being would have.
1 God has maximal greatness (has maximal excellence in every possible
world) is true unless it is self-contradictory.
2 God has maximal greatness is not self-contradictory. So:
3 God has maximal greatness is true.
4 If God has maximal greatness is true then God exists. So:
5 God exists.
The argument is plainly valid. Its form is:
1 P unless necessarily not-P.
2 Not necessarily not-P. So: